UC3842BN1 Просмотр технического описания (PDF) - ON Semiconductor
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UC3842BN1 Datasheet PDF : 20 Pages
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UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV
VCC
Vin
7(12)
5.0V Ref
8(14)
R
+
Bias
-
8(14)
R
Bias
5.0V Ref
R
+
-
7(11)
Q1
4(7)
2(3)
1.0M
R
+
-
Osc
+
1.0mA
2R
EA
R
1.0V
Osc
4(7)
+
VClamp
1.0 mA
S
Q
S
2(3)
EA
R2
2R
R
1.0V
R
Comp/Latch
Q
1(1)
R
C
R1 MPSA63
5(9)
6(10)
5(8)
3(5)
RS
1(1)
C
5(9)
tSoft-Start ≈ 3600C in µF
ǒ Ǔ VClamp Ă[Ă
1.67
R2
R1
)
1
Where: 0 ≤ VClamp ≤ 1.0 V
ƪ ƫ tSoftĆStart + * In
1
*Ă
VC
3ĂVClamp
ĂC
R1ĂR2
R1 Ă)Ă R2
Ipk(max)Ă
[Ă
VClamp
RS
Figure 24. Soft–Start Circuit
Figure 25. Adjustable Buffered Reduction of
Clamp Level with Soft–Start
VCC
Vin
(12)
VPin 5
[
RS Ipk rDS(on)
rDM(on) ) RS
5.0V Ref
+
-
If: SENSEFET = MTP10N10M
RS = 200
Then :Ă VPinĂ5Ă [Ă 0.075ĂIpk
+
-
S
(11)
G
(10)
D SENSEFET
S
K
M
Q
R
(8)
Comp/Latch
(5) RS
1/4 W
Power Ground:
To Input Source
Return
Control Circuitry Ground:
To Pin (9)
Virtually lossless current sensing can be achieved with the implementation of a
SENSEFET power switch. For proper operation during over-current conditions, a
reduction of the Ipk(max) clamp level must be implemented. Refer to Figures 23 and 25.
Figure 26. Current Sensing Power MOSFET
5.0V Ref
+
-
S
Q
R
Comp/Latch
VCC
Vin
7(12)
+
-
7(11)
Q1
6(10)
5(8)
3(5)
R
C
RS
The addition of the RC filter will eliminate instability caused by the leading
edge spike on the current waveform.
Figure 27. Current Waveform Spike Suppression
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